Experience
You must try to get as much experience as possible to survive the later levels of the game. Buy experience points in between levels, unless you have to spend it on other things to survive. Also, always destroy all monsters in the level. Try to get to level 10 by the end of the game.

Food
Save your money and do not buy too much food. If you are skilled, can complete the first three levels before becoming hungry. Also, find the food hidden in the levels rather than buying it.